1. Field of the Invention
The present invention relates generally to the field of telecommunications devices. More specifically, the present invention is directed to a method for processing transmitter and program related data in an FM RDS receiver and to a receiver for executing the method.
2. Description of the Related Art
The invention relates to a method for processing transmitter and program related data in an FM RDS receiver and to a receiver executing the method.
The FM RDS broadcasting standard is defined in xe2x80x98Specification of the Radio Data System FM RDS for VHF-FM Sound Broadcastingxe2x80x99 by the European Broadcasting Union (EBU), EBU document Tech 3244-E, March 1984 and updated in subsequent revisions thereof. Reference is made to this document for a correct understanding of the meaning and definition of the various terms and abbreviations used hereinafter in connection with the FM RDS standard.
An FM RDS receiver executing the above method is on itself known e.g. from European Patent 0 333 194. The known FM receiver is a dual tuner FM RDS receiver having a first or main tuner and a second or auxiliary tuner. The main tuner is used to tune the receiver to a broadcast transmitter station with a wanted audio program and to process the audio program signals for sound reproduction. If the transmitter transmits RDS data as well, then the main tuner will also extract the RDS data carried by the received RDS transmitter signal, in particular a list of alternative frequencies (AFs). Such list provide tuning data of transmitter frequencies carrying the same program as the one the receiver is actually tuned to. The auxiliary tuner is used to monitor the reception quality of the transmitter signals at each of those AFs. For this, the auxiliary tuner is sequentially switched to each AF in the AF list to measure the reception quality of the transmitter signals at the respective AFs. This reception quality information is stored in a memory and continuously updated in sequential scan cycles. On deterioration of the received transmitter signal the main tuner is automatically switched over in its tuning to the AF stored in the memory having highest reception quality.
The options in the above automatic switch-over of the tuning of the main tuner are limited to the correctly received and decoded AFs.
It is an object of the invention to remove this limitation and to increase the range of tuning selection options.
According to the invention a method for processing transmitter and program related data in an FM RDS receiver is therefore characterized by a band scanning search for detecting FM RDS transmitters exceeding a predetermined reception quality level, by storing in a first memory bank transmitter related data per each such transmitter, including the tuning data and a quality factor indicating the quality in reception thereof, by storing in a second memory bank program related FM RDS data per each received program identification code and by allocating to the transmitter data of each FM RDS transmitter stored in the first memory bank a linkage code defining the storage address within the second memory bank containing the program data carried by the relevant FM RDS transmitter.
By the measure according to the invention no use is made of FM RDS AF data. Instead, the second tuner is used to scan sequentially through the frequency band to search for any broadcasting transmitter station received with adequate RF signal reception quality, including FM RDS broadcast stations. Upon detection of such FM broadcasting transmitter station, the scanning is stopped to read the above transmitter related data into the first memory bank and in case of an FM RDS signal to read the FM RDS data into the second memory bank as well. The splitting in the storage of the transmitter related data and the program related data allows to make efficient use of storage capacity while preserving any tuning selection option for the user as will hereinafter be explained in more detail. The storage of RDS program data allows e.g. to provide AF switching without making use of the AF lists included in the RDS data and/or to extend the definition of alternative programs from strictly identical audio programs to non-identical programs within a certain RDS program category, such as PTY.
An FM RDS receiver executing the method according to the invention comprising first and second tuner circuits for receiving and processing respectively audio signals and FM RDS data, comprising tuning control means to vary the tuning frequency of the second tuner circuit over a frequency band to detect FM RDS transmitters received with a reception quality exceeding a predetermined quality threshold level, the first tuner circuit automatically switching over in its tuning from an actually received first FM RDS transmitter to a second FM RDS transmitter detected by the second tuner circuit when the reception quality of the first FM RDS transmitter decreases below a predetermined level characterized by a processing unit storing in a first memory bank per each selected FM RDS transmitter, transmitter related data including the tuning data and a quality factor indicating the reception quality thereof and in a second memory bank program related FM RDS data per each received program identification code and by allocating to the transmitter data of each FM RDS transmitter stored in the first memory bank a linkage code defining the storage address within the second memory bank containing the program data carried by the relevant FM RDS transmitter.
Preferably, the method is characterized in that the band scanning search is being repeated in subsequent scan cycles, the transmitter related data being updated with regard to its quality factor and being deleted from the first memory bank when the quality factor decreases below a predetermined quality threshold level.
An FM RDS receiver executing said preferred method is characterized in that the tuning control means controls the tuning of the second tuning circuit to repeat the band scanning search in subsequent scan cycles to update the quality factor of each detected transmitter, the storage locations in the first memory bank relating to transmitters decreasing in quality factor below a predetermined quality threshold level, being deleted.
This measure further improves the efficiency in the use of memory capacity without losing the information which transmitter frequency should be chosen in case the actually received transmitter signal decreases below said predetermined threshold level.
A further preferred method is characterized by an automatic tuning switch over from a first FM RDS transmitter to a second FM RDS transmitter, when the first FM RDS transmitter signal decreases below a predetermined threshold field strength level, the second FM RDS transmitter being selected from the FM RDS transmitters in the first memory bank having the same linkage code as the first FM RDS transmitter.
An embodiment of an FM RDS receiver executing the last mentioned further preferred method is characterized in that in selecting the second transmitter the processing unit is limited to FM RDS transmitters having the same linkage code as the first FM RDS transmitter signal.
By this measure the alternative frequencies (AFs), i.e. the transmitter frequencies carrying the same audio program as the one the first tuner circuit is actually tuned to, are not derived from the AF list included in the FM RDS data, but from those transmitter having the same linkage code attached thereto. The AF having highest reliability in reception quality, i.e. highest quality factor and/or field strength, can be determined very quickly.